Here's why:

* Fundamental frequency: This is the lowest frequency at which a string, air column, or other vibrating object naturally vibrates. It's the "base" sound you hear.

* Overtones/Harmonics: These are frequencies that are whole number multiples of the fundamental frequency. For example:

* The first overtone is twice the frequency of the fundamental.

* The second overtone is three times the frequency of the fundamental.

* And so on...

These higher frequencies contribute to the overall timbre (the unique sound quality) of a sound.

Example:

A guitar string might have a fundamental frequency of 100 Hz. Its first overtone would be 200 Hz, its second overtone 300 Hz, and so on. The combination of all these frequencies creates the rich, complex sound of a guitar.